1. Field of the Invention
This invention concerns a toothed-belt drive comprised of a toothed belt and a spur-gear meshing with the teeth of the belt. The force transmission between the belt and spur-gear takes place along the abutting faces of the teeth of the particular belt-drive part.
2. Description of the Prior Art
In a known toothed-belt drive of this kind, the force is ordinarily transmitted by means of flat or convex faces on the teeth of the toothed belt or the spur-gear. These faces can transmit only a limited force due to height limitations of the face of the teeth in relation to the design. The forces to be transmitted can only be increased to a minimal degree due to the limited surface area or size of the tooth's surface in light of the shearing and abrading forces exerted on the belt teeth. Toothed belt teeth are sometimes provided with small notches on the top surface of the teeth equal to about 10% of the tooth height. However, these small notches are not for the purpose of transmitting additionally larger forces, but instead serve to decrease the noise level during the operation of the toothed belt and to improve the meshing of the belt teeth with those of the spur-gear. Because of the small notch size, the notches do not allow force transmission.
SUMMARY OF THE INVENTION
It is the object of the invention to design a long lasting toothed belt drive that can absorb higher shearing and abrasive forces resulting from substantial force transmissions between a belt and the tooth without premature damage to the toothed belt. This is accomplished by having a toothed belt and spur gear interface such that the teeth of the toothed belt are each comprised of a recess including at least one notch dividing each recess into two portions. All interfacing surfaces of the toothed belt and the spur gear are curved.
In the invention, the belt teeth are each provided with a conically tapered recess which starts at the top surface of the tooth with curvature of the mutually opposite walls of the recesses corresponding to the curvature of the outer faces of the belt teeth and the recess depth being such so as to allow using the recess inner walls as the force-transmitting faces. These recesses are each engaged with a correspondingly designed projection of the spur-gear present between two spur-gear teeth.
By means of this design, both the shearing and abrasive forces are dispersed and the transmission forces are accordingly able to be substantially increased because they are transmitted not by one, but by two faces of the same tooth, the second face being formed by part of the recess wall.
The force transmission by the teeth of the toothed belt herein takes place over the entire tooth width just as in the conventional case, uniformly extending the force transmitting stresses across the width of the teeth.
The depth of the recess should be at least 50% of the height of the toothed belt, so as to assure effective force transmission.
In a preferred embodiment, the recess forms a comparatively large abutting surface of the faces of the belt teeth and the spur-gear. Consequently, the shearing and abrasive surface at the base of the teeth of the belt is retained, whereby the transmitted forces and the life of the toothed belt can be optimized.
If the recess are larger than the gaps between the individual teeth, then the tooth cross-section at the bottom of the tooth would be substantially degraded. Consequently, in yet another preferred embodiment, the recess should be about 70% to the tooth height. The increased surface area of the toothed belt drive increases the area upon which force can be transmitted and in turn reduces the polygonal effect on force transmission.
In the preferred embodiment, the head of the belt teeth shall rest at the bottom of the tooth gaps between two spur-gear teeth in order to reduce the so-called "polygon effect".
In another preferred embodiment, the projection of the spur-gear entirely fills the recess during meshing.
Additionally, the tooth width should be comparable to the pitch.